1. Field of the Invention
The present invention relates to a cooling system for turbocharged internal combustion engines. In particular, the present invention relates to a cooling system having a modified radiator wherein a portion of the liquid coolant may be bypassed around the radiator to provide temperature control, operating in series with a second radiator wherein a portion of the liquid coolant is subcooled before being utilized in the turbocharger aftercooler and wherein fan velocity is adjusted as a function of ambient air temperature and engine load. (Thermal stress in the radiator and subcooler are minimized by the incremental application of temperature change across two systems.)
2. Prior Art
The cooling system for an internal combustion engine is designed to remove heat caused by friction in the engine. One component of the cooling system is a radiator which passes liquid coolant in heat exchange with air in order to throw off or dissipate heat into the atmosphere.
Manipulation of the velocity of a fan or fans forcing air in heat exchange with the radiator will partially control the temperature of the coolant and, in turn, the engine.
The proper engine operating temperature is an important factor in efficient engine operation. At low ambient temperatures, engine operating temperature can actually be below the optimum operating temperature. In this case, the efficiency of the engine is decreased and the quantity of pollutants discharged will be increased due to inefficient performance.
The use of turbocharging to increase the power of an internal combustion engine has been known since at least the early part of this century. The air to be mixed with fuel to provide the proper air/fuel mixture is compressed prior to combustion in order to increase the number of molecules per given volume. The compressed charge that comes out of the turbocharger is not only denser but hotter as well. Since a cooler combustion mixture is desirable to enhance combustion efficiency and lower the quantity of exhaust pollutants, the combustion mixture may be passed in heat exchange with the liquid coolant after discharge from the radiator.
In many instances, however, the coolant temperature is only 10.degree. F. to 15.degree. F. below the engine operating temperature.
Applicant is aware of the following U.S. patents:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 3,516,231 George 3,841,064 Hitchiner et al. 4,325,219 Stang et al. 4,485,624 Melchior 4,517,929 Musick et al. 4,520,767 Roettgen et al. 4,550,692 Crofts, Sr. 4,563,983 Hayashi et al. 4,620,509 Crofts ______________________________________
In Hayashi (U.S. Pat. No. 4,563,983), the rate at which vapor from both the turbocharger intercooler and the engine coolant system is condensed in a common radiator in a manner to raise the pressure within the system and increase the boiling point of the coolant during low load modes such as urban cruising while lowering the pressure and boiling point in response to high speed/load engine operation.
George (U.S. Pat. No. 3,516,231) discloses an aftercooler used between the compressor and reservoir in an air supply line which cools the air from the compressor, filters out water and dirt, condenses moisture and oil vapors into liquids, automatically ejecting the contaminants every compressor cycle and automatically unloading the aftercooler to atmospheric pressure between each compressor cycle.
Hitchiner (U.S. Pat. No. 3,841,064) provides an aftercooler for cooling and cleaning compressed air.
Stang (U.S. Pat. No. 4,325,219) discloses a coolant system including a turbocharger and an aftercooler. Each loop further includes a temperature responsive flow control thermostat.
Melchior (U.S. Pat. No. 4,485,624) discloses a supercharged engine equipped with a cooling system including a radiator for the liquid cooling of the engine and a radiator for the supercharging air delivered by a turbocompressor.
Musick (U.S. Pat. No. 4,517,929) provides a self-adjusting cooling system for an internal combustion engine.
Roettgen (U.S. Pat. No. 4,520,767) provides a cooling system for a turbocharged diesel engine having an aftercooler and an oil cooler.
Crofts (U.S. Pat. No. 4,550,692) provides an engine cooling system wherein coolant is circulated through a circuit including an engine, a radiator and an aftercooler. Means are provided for automatically regulating the temperature of the coolant passing through the aftercooler.
Crofts (U.S. Pat. No. 4,620,509) provides a cooling system which selectively directs coolant through one of two circuits or simultaneously through both circuits dependent upon the temperature of the coolant. Also includes a thermostatically controlled primary valve.
Larsen (U.S. Pat. No. 4,697,551) provides a method and apparatus for quickly adjusting the coolant flow in a tuned, low-flow coolant system to maintain the temperature of air leaving an aftercooler.
While some of the foregoing disclose systems for controlling circulation of coolant, none of the prior art discloses a system of controlling the temperature of the coolant through bypassing a portion around the radiator, by directing a portion of the liquid coolant that has passed through the radiator to a subcooler prior to introduction to the turbocharging system, and, at the same time, controlling the fan speed in view of the ambient air temperature and the engine load. None of the prior art utilize series flow between heat exchange units to achieve incremental temperature changes which will permit lower charge-air coolant temperatures with lower thermal stress across the heat exchanger units.